1. Field of the Invention
This invention relates to millimeter wave integrated circuits (MIC's) and to methods of fabricating such circuits.
2. Description of the Prior Art
Millimeter wave integrated circuits are generally low power devices which are limited to small signal processing applications. Attempts to provide high power integrated circuits, e.g. for use in high frequency transmission systems, wherein passive matching components and active power components such as Gunn diodes have so far proved unsuccessful. These active and passive components have widely conflicting requirements. Thus a Gunn diode structure typically involves the fabrication of an n.sup.+ -n-n.sup.+ epitaxial layer on an n.sup.++ gallium arsenide substrate whereas millimeter wave integrated circuits require a high resistivity semi-insulating substrate to provide the necessary isolation of the circuit. To reduce thermal impedance thereby preventing overheating of the diode, it is then necessary to reduce the thickness of the MIC substrate. If this is done, however, the strip line loss of the MIC increases to an unacceptable value and the whole device becomes extremely fragile.